Shaping of a ground state rotational wavepacket by frequency-chirped pulses

0953-4075; A coherent rotational superposition state is produced in the ground vibronic level of N2 through the interaction of the molecule with the electric field vector of a nonresonant laser pulse. This rotational wavepacket is shaped with a linear frequency chirp of the laser field. The structural shape of the rotational coherences shows a strong dependence with the frequency-chirp amplitude. A comparison with a theoretical model allows the interpretation of the observed effects in terms of dephasing of the wavepacket induced by the laser phase distortion. Application of the presented results to the phase characterization of short XUV pulses is suggested.